Primary Feathers in Flight. 149 



from the north, northeast or northwest, hawks immediately 

 appear in large numbers. Records seem to show that these 

 birds utilize the wind as a means of migration, and that they 

 begin their migration movements independently of changes of 

 temperature that occur.* The hawks that were shot had 

 been migrating for hours, alternately soaring and coast- 

 ing, and were killed as they passed over one of the high 

 hills near the coast. During the migration, where a portion of 

 the journey is against the wind, if hawks approach a hill in 

 line of their flight, they usually coast with set wings and 

 descending pass rapidly over the crest of the hill close to the 

 ground. Having passed the crest of the hill they almost 

 invariably soar until they have ascended many hundred feet, 

 apparently using the upward air currents that exist on the 

 windward slope. They then again coast towards the next hill 

 that lies in the direction in which they are migrating. 



In a few places the coast line is at right angles to the direc- 

 tion of migration. At these points in the migratory route the 

 hawks often fly almost against the wind. Where the wind 

 is favorable the hawks migrate at an altitude of a thousand 

 feet or more. 



The observations at Paterson, IN. J., in the spring (Table III, 

 etc.) have been made when hawks are moving northward, 

 migrating in the manner just described. 



This brief description of the way in which the Falconidae 

 make their migrations has been given to show the conditions 

 under which the observations recorded in this paper have 

 been made. All the hawks obtained were killed during the 

 migrations. 



An examination of Table I shows the following significant 

 facts : — 



Number of perfect wings of 23 specimens of one species 



examined 40 



Number of wings found with some primaries interlocked- 40 



Number of wings with five (all) primaries interlocked 10 



Number of wings with four primaries interlocked 8 



Number of wings with three primaries interlocked 11 



Thus 29 out of 40 wings were found to have an average of 

 76 per cent of their emarginate primaries interlocked. 



Total number of emarginate primaries of perfect wings 200 



Total number of emarginate primaries of perfect wings 



interlocked 134 



Percentage of primaries found interlocked ..67.0$ 



*0. C. Trowbridge: Eelation of Wind to Bird Migration, Arner. Nat., 

 xxxvi, 429, Sept., 1902. 



